The development of a human respiration carbon dioxide (CO2) measurement device to evaluate cardiorespiratory status inside and outside a hospital setting has proven to be a challenging area of research over the few last decades. Hence, we report a real-time, user operable CO2 measurement device using an infrared CO2 sensor (Arduino Mega2560) and a thin film transistor (TFT, 3.5″), incorporated with low pass (cut-off frequency, 10 Hz) and moving average (span, 8) filters. The proposed device measures features such as partial end-tidal carbon dioxide (EtCO2), respiratory rate (RR), inspired carbon dioxide (ICO2), and a newly proposed feature-Hjorth activity-that annotates data with the date and time from a real-time clock, and is stored onto a secure digital (SD) card. Further, it was tested on 22 healthy subjects and the performance (reliability, validity and relationship) of each feature was established using (1) an intraclass correlation coefficient (ICC), (2) standard error measurement (SEM), (3) smallest detectable difference (SDD), (4) Bland-Altman plot, and (5) Pearson's correlation (r). The SEM, SDD, and ICC values for inter- and intra-rater reliability were less than 5% and more than 0.8, respectively. Further, the Bland-Altman plot demonstrates that mean differences ± standard deviations for a set limit were 0.30 ± 0.77 mmHg, -0.34 ± 1.41 mmHg and 0.21 ± 0.64 breath per minute (bpm) for CO2, EtCO2 and RR. The findings revealed that the developed device is highly reliable, providing valid measurements for CO2, EtCO2, ICO2 and RR, and can be used in clinical settings for cardiorespiratory assessment. This research also demonstrates that EtCO2 and RR (r, -0.696) are negatively correlated while EtCO2 and activity (r, 0.846) are positively correlated. Thus, simultaneous measurement of these features may possibly assist physicians in understanding the subject's cardiopulmonary status. In future, the proposed device will be tested with asthmatic patients for use as an early screening tool outside a hospital setting.
We prospectively evaluated the use of a simple 3-Minute Respiratory Exerciser Test (3MRET) that estimates perception of dyspnea to identify patients at risk of asthma exacerbations. A total of 146 stable asthmatics (42 under-perceivers, 69 normal perceivers, and 35 over-perceivers) received follow-up for 12 months. The mean (SD) unscheduled visits to doctors among under-, normal, and over-perceivers were 1.8 (1.2), 2.2 (1.8), and 3.1 (2.3), respectively (p = 0.008). The mean (SD) hospital admissions among the groups were 1.3 (0.5), 1.2 (0.6), and 1.7 (1.3), respectively (p = 0.026). Compared to normal perceivers, over-perceivers had increased risks of unscheduled visits (OD: 5.12; 95% CI = 1.59 to 16.47) and hospital admissions (OD: 0.31; 95% CI = 0.23 to 0.41), defined as > or =2 events in 12 months. The association between over-perceiver and unscheduled visits remained significant after adjusting for forced expiratory volume in 1 second (FEV(1)). Sensitivity and specificity of over-perceivers are 77% and 47%, respectively, for unscheduled visits and 37% and 78%, respectively, for hospital admissions, with significantly better area under ROC for unscheduled visits (0.67 [95% CI = 0.56 to 0.77]; p = 0.003) than for hospital admissions (0.58 [0.471 to 0.70]; p = 0.127). We conclude that the 3MRET may have a role in identifying asthmatic patients with over-perception of dyspnea at risk of clinically important asthma exacerbations.